The evaluation of reference points and stock productivity in the context of alternative indices of stock reproductive potential

Abstract

In this study, we explore the impact of four alternative indices of reproductive potential (RP) on perceptions of population productivity for eight fish populations across the North Atlantic. The four indices of RP included increasing biological complexity, adding variation in maturation, sex ratio, and fecundity. Perceptions of stock productivity were greatly affected by the choice of index of RP. Population status relative to reference points, RP per recruit, and projections of population size all varied when alternative indices of RP were used. There was no consistency in which index of RP gave the highest or lowest estimate of population productivity, but rather, this varied depending on how much variation there was in the reproductive biology of the population and the age composition. Estimates of sustainable harvest levels and recovery time for depleted populations can vary greatly depending on the index of RP.

Reproductive potential of Yellowfin Tuna (Thunnus albacares) in the western Indian Ocean

“…Sampling was done by scientifi c observers during 3 surveys conducted on board a commercial purse seiner in the western Indian Ocean during 2009 and2010 (Fig. 1).…”

“…The mean batch fecundity for females 79-147 cm FL was estimated at 3.1 million oocytes, and the mean relative batch fecundity was 74.4 oocytes per gram of gonad-free weight. Our results, obtained with techniques defined more precisely than techniques used in previous studies in this region, provide an improved understanding of the reproductive cycle of Yellowfin Tuna in the western Indian Ocean.Knowledge of reproductive traits is important for understanding population dynamics, including a population's resilience to fi shing (Schaefer, 2001;Murua and Motos, 2006;Morgan et al, 2009). As alternatives to the traditional spawning stock biomass (SSB), reproductive potential indices have been proposed in which basic reproductive parameters are included as important factors that affect population productivity (Trippel, 1999;Morgan et al, 2009).…”

“…Knowledge of reproductive traits is important for understanding population dynamics, including a population's resilience to fi shing (Schaefer, 2001;Murua and Motos, 2006;Morgan et al, 2009). As alternatives to the traditional spawning stock biomass (SSB), reproductive potential indices have been proposed in which basic reproductive parameters are included as important factors that affect population productivity (Trippel, 1999;Morgan et al, 2009).…”

“…As alternatives to the traditional spawning stock biomass (SSB), reproductive potential indices have been proposed in which basic reproductive parameters are included as important factors that affect population productivity (Trippel, 1999;Morgan et al, 2009). These parameters include sex-ratio, the age and size of females, maturation ogive, fecundity, fi sh condition, and reproductive history.…”

Modelling the spatio-temporal distribution of age-1 Bay of Biscay anchovy (<i>Engraulis encrasicolus</i>) at spawning time

“…Egg production can be attributed to the first or repeated spawners and it can be determined whether different age structures at spawning affect recruitment survival (Marteinsdottir and Thorarinsson 1998). Older and larger females might have higher per capita fecundity (Kennedy et al 2007, Morgan et al 2009) and are often able to produce higher-quality eggs (Brooks et al 1997), which results in higher survival (Marteinsdottir and Steinarsson 1998).…”